This invention relates to a multi-magnification document reproduction machine, and more particularly, to an imaging system adapted to produce anamorphically reduced or enlarged copies of an original document.
The concept of anamorphically reducing or enlarging an image via a velocity mis-match of a scanned image to a moving recording medium is known in the photographic and copy art. U.S. Pat. Nos. 3,126,809, 4,111,551 and 3,967,898 associated with the photographic art, disclose the production of copies from a negative by elongating or reducing the copy in a single direction. In 4,111,551 a negative and a photosensitive film are separately transported at different linear speeds past an elongated pair of drive rollers. The extent of image compression or elongation can be varied continuously by means of a differential speed drive mechanism interconnecting the drive roller. In 3,126,809, a negative and print paper are moved relative to each other while the negative is being illuminated through a moving mode with a light slit. In 3,967,898, a predetermined amount of distortion in one direction is produced by varying the relative motion of a film image sheet and a superimposed photosensitive material sheet across a light slit.
An anamorphic scanning system is also disclosed in U.S. Pat. No. 3,861,797. An original is reproduced in one direction at the original size and then elongated or compressed in a second direction. An original document is placed on a movable platen and illuminated by a light source so as to cause an image to be projected by a lens beneath the platen through a pair of slits onto a sensitive film disposed in an image plane. The relative speed of the platen and the film are varied to obtain the desired uni-directional magnification.
The resolution requirements for reproducing documents at varying magnification values have hitherto required an optical system in which a projection lens is moveable along an optical path, is conjunction with repositioning of mirrors. Alternatively, a zoom lens assembly in used having internal lens elements movable with respect to each other with the entire lens assembly also movable along an optical path. These conventional magnification imaging systems are relatively expensive due to the mechanism for maintaining total conjugate and the cost of the projection lenses. Anamorphic magnification has suggested the possibility of producing reduced and/or enlarged copies without the need for the conventional, expensive optical systems described above. The main problem to be overcome is to maintain copy resolution while anamorphically scanning a document and, in effect, producing a distorted image in the scan direction. The solution to this problem, according to one aspect of the present invention, has been found to lie in narrowing the scan slit width at the photosensitive output medium from the 12 mm, typical with conventional lens systems, to a width of about 1 mm or less. The narrower the slit width, the sharper the anamorphic image formed on the output medium. However, with the narrowing of the slit width, exposure is reduced requiring an increase in illumination requirements. Any practical system therefore has to be devised to optimize these two crucial factors. A third requirement is that there must be true two-dimensional reduction or enlargement of a quality equal to conventional multi-magnification system e.g. that the final copy be isomorphic. Applicants by this invention have achieved these goals, as will be described below.
There are additional prior art disclosures in the copier art disclosing anamorphic magnification imaging systems. For example, U.S. Pat. No. 4,583,846 discloses a slit exposure type machine which regulates the differential speeds of the scanning and recording medium in a known manner. The resolution of the anamorphically reduced or enlarged image is maintained by the introduction of a rotatable triangular shaped prism into the optical path between a projection lens and the recording medium. Another type of anamorphic imaging system is disclosed in U.S. Pat. No. 4,536,084. In this system, a conventional lens is used to normally copy documents in a 1X magnification. For a magnification change, an auxiliary anamorphic lens system is introduced into the optical path, the auxiliary system having different imaging magnifications in orthogonal directions. A third type of anamorphic magnification is briefly disclosed in U.S. Pat. No. 4,194,827, column 7, lines 39-40. The imaging system for the photocopy machine comprises a line or array of parallel coherent optical fibers, the ends of which are in virtual contact with an original document and a photosensitive copy sheet. The document is illuminated by a light source directing light through an optical element attached to the fibers. The imaging system utilizes a narrow exposure slit and, in column 7, it is suggested that the speed of the documents relative to the speed of the photosensitive record medium could be varied to provide variable enlargement or reduction of the copy along the direction of travel. Images formed by this system are "wrong reading" and require an additional transfer step.
These previous, prior art anamorphic systems, either have disadvantages and/or do not fulfill all of the requirements for a fully-realized, multi-magnification copier. The system of U.S. Pat. No. 4,583,846 provides for anamorphic magnification in a single direction and requires the use of a prism to maintain adequate resolution. U.S. Pat. No. 4,536,084 requires the use of a second imaging system to be used in conjunction with a 1X projection lens, a costly alternative requiring additional machine space. The imaging system of 4,194,827 does not disclose producing final copies magnified in both dimensions and is further disadvantaged by forming a "wrong-reading" image on the recording medium.
The present invention is therefore directed to a scanning system which, in a preferred embodiment, utilizes a linear gradient index lens array, inherently having a small effective slit width, to project an image of an original onto an imaging plane. The lens may comprise a plurality of gradient index lenses assembled into an array, known conventionally as a SELFOC (TM) lens array. The lens array has a characteristically narrow image plane irradiance profile width of 3-6 mm which is further reduced, according to the present invention, by a narrow slit positioned between the lens and the recording medium. Documents may be copied at a conventional 1:1 ratio. Anamorphic reduction or enlargement of the copy is achieved by varying the ratio of the speeds of the document and image plane relative to the lens array during the scan/exposure cycle. The document is illuminated by an optimally designed illumination system to provide the exposure necessary to maintain the desired resolution through typical compression (reduction) or elongation (enlargement) ranges of .+-.50%. According to another aspect of the invention, two-dimensional (isomorphic) reduction or enlargement is enabled by a two-pass operation which includes using a copy which has an image anamorphically magnified in a first direction as an original which is then rotated 90.degree. relative to the scan direction and scanned, anamorphically, a second time to form the final output copy. More particularly, the invention is directed to a scanning system in a reproduction apparatus which transmits an image of an original document lying in an object plane onto a photosensitive image plane, said image being enlarged or reduced in at least one scanning dimension, said system comprising:
an illumination means adapted to provide an intense narrow beam of light to successive portions of the documents to be copied,
a linear gradient index lens array arranged in the optical path so as to project light reflected from said document during said scan, said lens array forming an image plane irradiance profile of first width d.sub.1
means for scan/illuminating said document at a speed which is selectively changeable relative to the speed of said image plane and
a slit assembly attached to the output face of said lens array, and said image plane, said slit assembly having a slit aperture therethrough, said slit aperture having a width d.sub.2 less than said width d.sub.1.